CITRUS scab: its cause and control. 



11 



an abundance of scrapings from citrus-scab lesions not previously 

 disinfected were placed in sterile Petri dishes, covered with glycerin 

 agar or potato-dextrose agar, and held at room temperature for 10 

 or 15 days before making final records. Table 2 gives the result of 

 these isolation tests made for the most part in the laboratory at 

 Orlando, Fla. 



Table 2. — Results of isolation tests of citrus-scab fungits from citrus fruit and leaves. 



Tests op Leaves. 



Date of isolation. 



Host. 



Growth developed. 



Remarks. 



Dec 11 1916 



Grapefruit ... 



Spring, 1916 



Very many colonies 



Do 



Round orange 



do 



Many colonies. 



Feb. 14, 1917 



Grapefruit 



October, 1916 



Very many colonies. 



Feb. 15, 1917 



King orange 



Spring, 1916 



Do. 



July 27, 1917. 



Satsuma orange 



Sour orange 



Spring, 1917 



Do. 



Feb 10 1918 



-do... . . 



Many colonies. 



Do . 



Rough lemon 



do 



Do 



Grapefruit 



do 



Do. 



Feb. 20, 1919 



Sour orange 



Spring, 1918 



Very many colonies. 



Do 



Rough lemon 



do .- 



Do. 



Do ... 



Grapefruit 



do 



Do. 



Feb. 10, 1920 



Tangelo 



SnTmrifir 1919, 



Do. 



Do ... 



Calamondin 



do...' 



Do. 



Do 



Sweet bittersweet 



.do... 



Do. 



Oct. 24, 1920. 



do 



Spring, 1920 



Many colonies. 



Nov. 5, 1920 



Sour orange . . 



.do... 



Nov. 19, 1920 



do 



do 



Do. 



Feb. 6, 1921.. 



Grapefruit 



. ..do 



Do. 



Mar. 8, 1921 



do 



do 



Do. 



May9, 1921 



.do 



do 



Do. 











Tests of Feuit. 



Date of isolation. 



Host (grapefruit). 



Fruit set. 



Remarks. 



Feb. 15, 1917 



J-inch diameter 



Green, 1 J inches diam- 

 eter. 



Green, 2 inches diam- 

 eter. 



2J inches diameter 



December, 1916 



March, 1920 



Very many colonies. 

 Do. 



May 27, 1920 



June 10, 1920... 



.do. 





June 23, 1920 



do 



Do. 



Do 



...do 



do 



Do. 



July 20, 1920 



3 J inches diameter 



.. ..do. . . 



Do. 



Oct. 24, 1920 



Half colored 



do 



Do. 



Nov. 5, 1920 



do 



do 



Do. 



Nov. 19, 1920 



Three-fourths colored. . 

 Mature 



-do... 



do 



Do. 



Feb. 6, 1921 



Spring, 1920. 



Do. 



Mar. 8, 1921 



-do. 



Do. 



Mar. 9, 1921 



do 



.do 



Do. 



July 23, 1918 



Ripe 



.. ..do 



December, 1917 



December, 1919 



Do. 



Feb. 10, 1920 



Do. 









These tests show that when once the scab fungus enters a leaf, it 

 can persist there throughout the winter. This finding is corroborated 

 by a large number of field observations in which new flushes devel- 

 oping in close proximity to hold-over lesions were seriously affected 

 by scab while more distant flushes were scab free. 



The isolation experiments further show that the causal organism 

 does not persist for any great length of time in fruit. It seems rea- 

 sonable to conclude from cultural data and field observations that 

 the disease is seldom if ever carried over winter on fruit set in the 

 spring or summer. 



